2.时间状语：by the time of; by the end of+时间短语(将来);by the time+从句(将来)

3.基本结构：主语+be going to/will/shall + have+p.p(过去分词)+其它

 4例句：

By the time you get back,great changes will have taken place in this area.

到你回来的时候，就将发生巨大的变化。